The present invention relate to a method for detecting the resonance frequency of an electrical oscillation circuit, for example of a starter oscillation circuit for high-pressure gas discharge lamps.
In a method of this type known from European Published Patent Application 271 369, the resonance frequency during the starting process of a gas discharge lamp is determined by frequency sweep. In so doing, a frequency ramp is continuously run through from a minimum value to a maximum one and back again. At each passage through the resonance frequency, the oscillation circuit is excited for a brief time. A different method provides for passage through a frequency ramp. When the resonance frequency is reached, the oscillation circuit begins to oscillate. An additional possibility is to provide for a design of a self-oscillating circuit in which the resonance circuit itself sets the oscillating frequency.
The disadvantage of all of these known methods is that they do not operate satisfactorily in all respects and/or are quite expensive and require the costly use of special components.
In contrast, the advantage of the method according to the present invention for detecting the resonance frequency of an electrical oscillation circuit that it makes it possible to detect or determine and find the resonance frequency, subject to tolerance, of an electrical oscillation circuit to be triggered in a short time and at low expense.
According to the underlying concept of the present invention, the frequency search is undertaken in a search run with individual sampling tests, a specific, fixed frequency is used in the sampling tests, and each fixed frequency is selected and used according to a specified search pattern.
The present invention makes a purely controlled, time-optimized search method available which eliminates the need for a self-oscillating circuit, which is difficult to implement, especially in the very high frequency range. Moreover, it is not even necessary to recognize whether movement is toward or away from the actual resonance frequency during the search. Such recognition would otherwise have to be made via phase detection, which is associated with greater hardware expense. If a microcontroller is provided in the control unit containing the electrical oscillation circuit, which may very often be the case today, then the otherwise necessary hardware circuits can be eliminated and replaced by software functions which are carried out by the microcontroller.
According to a particularly advantageous further development of the present invention, the first sampling test in the search pattern is carried out at the mean frequency fmitt, the mean frequency fmitt being the mean of the minimum fmin, and maximum fmax possible resonance frequency.
According to a particularly advantageous embodiment of the method according to the present invention, the frequency range is divided into equidistant steps xcex94f between the minimum fmin and maximum fmax possible resonance frequency, and the number of steps is selected taking the frequency range to bandwidth ratio of the oscillation circuit into account.
In a particularly suitable further development of this embodiment of the method according to the present invention, the second sampling test is undertaken at the fixed frequency fmitt+xcex94f and the third sampling test at the fixed frequency fmittxe2x88x92xcex94f, or also vice versa.
According to an additional particularly advantageous embodiment of the present invention, the method provides that the additional sampling tests are carried out at test frequencies
fmitt+2xcex94f, fmittxe2x88x922xcex94f;
fmitt+3xcex94f, fmittxe2x88x923xcex94f;
fmitt+4xcex94f, fmittxe2x88x924xcex94f;
fmitt+5xcex94f, fmittxe2x88x925xcex94f, etc.
According to an additional very suitable embodiment of the present invention, the resonance frequency fres determined in a search run is stored in memory and, as a quasi-learning frequency flern, is available as a starting frequency for a subsequent search run. In the next search operation, for example, after the control unit containing the oscillation circuit is switched off and on, the search operation does not start with fmitt but rather with the previously learned and stored value flern.
According to a particularly advantageous further development of this embodiment of the present invention, learning frequency flern, is stored in a non-volatile memory. In a further embodiment, learning frequency flern may additionally be stored in an EEPROM cell of a microcontroller, it being possible to store learning frequency flern as a control voltage for a voltage-controlled oscillator. It is particularly advantageous to store the frequency value determined in the most recent search run each time.
In a further improvement of these embodiments of the method according to the present invention, resonance frequency fres which is determined in a search run is only stored once again as learning frequency flern if the interval between the old stored value and the newly determined value exceeds a specified amount. This can bring about a reduction of the number of the newly stored values. This is particularly advantageous if the number of the starting operations of the control unit in which the oscillation circuit is installed is greater than the number of the maximum allowable number of write cycles of the non-volatile data memory.
According to a different advantageous further development of the method according to the present invention, if the limits defined by the minimum fmin and maximum fmax possible resonance frequency are reached during a search run, the subsequent search is only carried out in the direction of the respective other limit.
A further suitable embodiment of the method according to the present invention provides that after a completed unsuccessful search run, it is repeated and started again with the stored learning frequency flern, if necessary. This embodiment is of particular benefit in those applications in which the detection of resonance frequency fres is evaluated according to whether a desired sparkover has taken place when the electrical oscillation circuit begins to oscillate, for example, in a high-pressure gas discharge lamp to be ignited and in which sparkover and consequently ignition does not take place in the first attempt by the occasional occurrence of high sparkover voltages in spite of a precisely detected resonance frequency fres.
A further advantageous modification of the method according to the present invention provides that the search is initially not run completely but rather only in a limited search range, in particular from learning frequency flernxc2x1n*xcex94f, n being selected so that the typically occurring drift of the resonance frequency is located within the selected search range. A useful further development of this modification provides that if the success criterion is not found within the limited search range, the search is initially carried out a few more times only in the limited search range before the search is extended, if necessary, to the entire search range. This is also of particular advantage in this case if the number of starting operations of the control unit in which the oscillation circuit is located is greater than the number of the maximum allowed write cycles of the non-volatile data memory. According to a particularly suitable embodiment of this further development, the limited search range can be extended step-by-step to the maximum search range after each unsuccessful search series.